Thrombotic complications are a major cause of death in the industrialized world. Examples of these complications include acute myocardial infarction, unstable angina, chronic stable angina, transient ischemic attacks, strokes, peripheral vascular disease, preeclampsia/eclampsia, deep venous thrombosis, embolism, disseminated intravascular coagulation and thrombotic cytopenic purpura. Thrombotic and restenotic complications also occur following invasive procedures, e.g., angioplasty, carotid endarterectomy, post CABG (coronary artery bypass graft) surgery, vascular graft surgery, stent placements and insertion of endovascular devices and prostheses, and hypercoagulable states related to genetic predisposition or cancers. It is generally thought that platelet aggregates play a critical role in these events. Blood platelets, which normally circulate freely in the vasculature, become activated and aggregate to form a thrombus from disturbed blood flow caused by ruptured atherosclerotic lesions or by invasive treatments such as angioplasty, resulting in vascular occlusion. Platelet activation can be initiated by a variety of agents, e.g., exposed subendothelial matrix molecules such as collagen, or by thrombin which is formed in the coagulation cascade.
An important mediator of platelet activation and aggregation is ADP (adenosine 5′-diphosphate) which is released from blood platelets in the vasculature upon activation by various agents, such as collagen and thrombin, and from damaged blood cells, endothelium or tissues. Activation by ADP results in the recruitment of more platelets and stabilization of existing platelet aggregates. Platelet ADP receptors mediating aggregation are activated by ADP and some of its derivatives and antagonized by ATP (adenosine 5′-triphosphate) and some of its derivatives (Mills, D. C. B. (1996) Thromb. Hemost. 76:835-856). Therefore, platelet ADP receptors are members of the family of P2 receptors activated by purine and/or pyrimidine nucleotides (King, B. F., Townsend-Nicholson, A. & Burnstock, G. (1998) Trends Pharmacol. Sci. 19:506-514).
Recent pharmacological data using selective antagonists suggests that ADP-dependent platelet aggregation requires activation of at least two ADP receptors (Kunapuli, S. P. (1998), Trends Pharmacol Sci. 19:391-394; Kunapuli, S. P. & Daniel, J. L. (1998) Biochem. J. 336:513-523; Jantzen, H. M. et al. (1999) Thromb. Hemost. 81:111-117). One receptor appears to be identical to the cloned P2Y1 receptor, mediates phospholipase C activation and intracellular calcium mobilization and is required for platelet shape change. The second platelet ADP receptor important for aggregation mediates inhibition of adenylyl cyclase. Based on its pharmacological and signaling properties this receptor has been provisionally termed P2YADP (Fredholm, B. B. et al. (1997) TIPS 18:79-82), P2TAC (Kunapuli, S. P. (1998), Trends Pharmacol. Sci. 19:391-394) or P2Ycyc (Hechier, B. et al. (1998) Blood 92, 152-159). More recently, molecular cloning of this receptor (Hollopeter, G. et al. (2001) Nature 409: 202-207) has revealed that it is a new member of the G-protein coupled family and is the target of the thienopyridine drugs ticlopidine and clopidogrel. The nomenclature given to this receptor is P2Y12.
Various directly or indirectly acting synthetic inhibitors of ADP-dependent platelet aggregation with antithrombotic activity have been reported. The orally active antithrombotic thienopyridines ticlopidine and clopidogrel inhibit ADP-induced platelet aggregation, binding of radiolabeled ADP receptor agonist 2-methylthioadenosine 5′-diphosphate to platelets, and other ADP-dependent events indirectly, probably via formation of an unstable and irreversible acting metabolite (Quinn, M. J. & Fitzgerald, D. J. (1999) Circulation 100:1667-1667). Some purine derivatives of the endogenous antagonist ATP, e.g., AR-C (formerly FPL or ARL) 67085MX and AR-C69931Mx, are selective platelet ADP receptor antagonists which inhibit ADP-dependent platelet aggregation and are effective in animal thrombosis models (Humphries et al. (1995), Trends Pharmacol. Sci. 16, 179; Ingall, A. H. et al. (1999) J. Med. Chem. 42, 213-230). Novel triazolo [4,5-d]pyrimidine compounds have been disclosed as P2T-antagonists (WO 99/05144). Tricyclic compounds as platelet ADP receptor inhibitors have also been disclosed in WO 99/36425. The target of these antithrombotic compounds appears to be P2Y12, the platelet ADP receptor mediating inhibition of adenylyl cyclase.
Despite these compounds, there exists a need for more effective platelet ADP receptor inhibitors. In particular, there is a need for platelet ADP receptor inhibitors having antithrombotic activity that are useful in the prevention and/or treatment of cardiovascular diseases, particularly those related to thrombosis.
In addition, while biological activity is a sine non qua for an effective drug, the compound must be capable of large scale manufacturing and the physical properties of the compound can markedly impact the effectiveness and cost of a formulated active ingredient. Salts of acidic and basic compounds can alter or improve the physical properties of a parent compound. These salt forming agents, however, must be identified empirically by the pharmaceutical chemist since there is no reliable method to predict the influence of a salt species on the behavior of a parent compound in dosage forms. Effective screening techniques, which potentially could simplify the selection process, are unfortunately absent (G. W. Radebaugh and L. J. Ravin Preformulation. In, Remington: The Science and Practice of Pharmacy; A. R. Gennaro Ed.; Mack Publishing Co. Easton, Pa., 1995; pp 1456-1457).
Amorphous and different crystalline solid/polymorphic forms of salts are frequently encountered among pharmaceutically useful compounds. Polymorphism is the ability of any element or compound to crystallize as more than one distinct crystalline species. Physical properties including solubility, melting point/endotherm maximum, density, hardness, crystalline shape and stability can be quite different for different forms of the same chemical compound.
Crystalline solid and amorphous forms may be characterized by scattering techniques, e.g., x-ray diffraction powder pattern, by spectroscopic methods, e.g., infra-red, solid state 13C and 19F nuclear magnetic resonance spectroscopy and by thermal techniques, e.g, differential scanning calorimetry or differential thermal analysis. Although the intensities of peaks in the x-ray powder diffraction patterns of different batches of a compound may vary slightly, the peaks and the peak locations are characteristic for a specific crystalline solid or amorphous form. Additionally, infrared, Raman and thermal methods have been used to analyze and characterize crystalline and solid amorphous forms. Solid and amorphous forms may be characterized by data from the X-ray powder diffraction pattern determined in accordance with procedures which are known in the art (see J. Haleblian, J. Pharm. Sci. 1975 64:1269-1288, and J. Haleblain and W. McCrone, J. Pharm. Sci. 1969 58:911-929). Although the intensities of peaks in the x-ray powder diffraction patterns of different batches of the compounds may vary slightly, the peaks and the peak locations are characteristic for a specific crystalline solid form.
The problem which must be solved is to identify a suitable salt and form which (i) possesses adequate chemical stability during the manufacturing process, (ii) is efficiently prepared, purified and recovered, (ii) provides acceptable solubility in pharmaceutically acceptable solvents, (iii) is amenable to manipulation (e.g. flowability and particle size) and formulation with negligible decomposition or change of the physical and chemical characteristics of the compound, (iv) exhibits acceptable chemical stability in the formulation. In addition, salts and forms containing a high molar percent of the active ingredient are highly desirable since they minimize the quantity of material which must be formulated and administered to produce a therapeutically effective dose. These often conflicting requirements make identification suitable salts a challenging and important problem which must be solved by the skilled pharmaceutical scientist before drug development can proceed in earnest.
Therefore, there is a need for compounds and salts and amorphous and crystalline solid forms of these compounds of the invention and an efficient process for producing the compounds, salts and crystalline solid forms of the compounds of the invention. Solutions to the above difficulties and deficiencies are needed before compounds become effective for routine treatment of thrombosis.
Polyaryl compounds generally are highly crystalline, poorly water soluble and hydrophobic, resulting in difficulties in the preparation of pharmaceutical formulations and problems associated with bioavailability. Accordingly, efforts were made to discover other forms of compounds of the invention and to investigate the properties thereof. There were discovered crystalline solid forms of salts of compounds of the invention. The present invention fulfills the above needs by providing polymorphs and methods for treating and preventing thrombosis, while presenting a better adverse effect profile.